Municipalities have waste treatment facilities to treat vast quantities of sewage. One product of the treatment process is sewage sludge. This type waste material is typically banned from landfill sites because of the risk of bacterial contamination of soil, bodies of water, and groundwater. This sludge must be decomposed in some manner so as to render it harmless to the environment. The advantages of composting organic materials to provide fertilizers and soil additives are well-known. The length of time and amount of ground space required in traditional backyard gardening techniques of composting are prohibitive for the large volume of sewage sludge generated by a municipality sewage treatment facility. Several processes have been developed to decompose sewage sludge to a satisfactory condition for exposure to the environment.
One such process measures the O.sub.2 content of waste air evacuated from a reaction vessel so that the aeration air flow may be adjusted at any time during the process to the level required for optimum composting. Another such process controls the throughput rate of the aeration air flowing through a reaction vessel such that the O.sub.2 content or the corresponding CO.sub.2 content of the waste air takes a desired value set externally. A third known process does not adjust the throughput rate of the aeration air, but rather fixedly sets the throughput rate without consideration to the O.sub.2 or CO.sub.2 contents.
These processes may compost sewage sludge to an environmentally safe level, but they require either multiple vessels, significant amounts of land, or great lengths of time to obtain these results. What is needed is a process utilizing a single vessel capable of quickly decontaminating sewage sludge by bacterial action to an environmentally safe level as specified by the Environmental Protection Agency such that the sludge is decontaminated and may be processed further without the need for expensive infrastructure.